1. Field of the Invention
The present invention relates to a construction of a solenoid valve circuit for controlling hydraulic pressure in an automatic transmission for a vehicle.
2. Description of the Prior Art
An automatic transmission for a vehicle has the combination of a planetary gear mechanism and a plurality of engaging elements such as clutch, brake or the like which are actuated by hydraulic pressure, and the combination of engagement and release of the engaging elements achieve a plurality of gear positions which respectively provide predetermined gear ratios.
The engaging elements are controlled by controlling line pressure with a shift valve in a control valve unit and by supplying the line pressure to the respective engaging elements. The shift valve is switched by hydraulic pressure controlled from a constant pilot pressure by a solenoid valve which is actuated by a control signal from a shift control system.
The control of pilot pressure by the solenoid valve is performed by controlling drain of a working fluid which has passed through an orifice by the solenoid valve, as in a hydraulic circuit disclosed in Japanese Patent Application Laid-open No. 1-199044.
More specifically, in this hydraulic circuit, line pressure from a manual valve 50, as shown in FIG. 2, is fed to a forward clutch F/C through an oil passage 51 and at the same time fed to a servo apply chamber of a brake B through a shift valve 52 provided in the middle of the oil passage 51. A control port of the shift valve 52 is in communication with an oil passage 55 extending from a pilot pressure valve 54, and an orifice 56 is provided in the middle of the oil passage 55. Moreover, a drain port 57 is provided on the downstream side of the orifice 56, that is, on the side of the shift valve 52, and drain of the working fluid is controlled by a solenoid valve 58. In many cases, the drain port 57 is provided in the solenoid valve 58.
As shown in FIG. 3, the conventional solenoid valve circuit including the orifice 56 and the solenoid valve 58, as described above, is arranged such that a separate plate 63 disposed between an upper body 61 and a lower body 62, which construct the control valve unit, is provided with a small aperture acting as the orifice 56, through which a working fluid supplied from the pilot pressure valve to the lower body 62 is guided to the upper body 61, and such that the solenoid valve 58 is disposed near the orifice 56 of the upper body 61. Moreover, drain of oil pressure on the side of the upper body 61 is controlled by the solenoid valve 58 to act as output pressure.
In the construction of such a solenoid valve circuit, however, the separate plate 63 is disposed between the upper body 61 and the lower body 62 to form the orifice 56, and the upper body 61 and the lower body 62 between which the separate plate 63 is arranged define oil passages. Therefore, even in case where it is desired to put together the pilot pressure valve and the solenoid valve 58 or the like into one of the upper body 61 and the lower body 62, the pilot pressure valve and the solenoid valve 58 need to be arranged opposite each other, having the separate plate 63 between them, whereby the degree of freedom in positions for mounting these valves becomes low. For example, if both the pilot pressure valve and the solenoid valve 58 are placed in the upper body 61, it is required to form a bypass passage leading from the pilot pressure valve to the oil passage on the side of the lower body 62.
Moreover, in case of adjusting the output pressure characteristics, to change the orifice 56, it is required to dismount the solenoid valve circuit and replace the separate plate 63, and thus this adjustment operation is difficult.
The present invention has been made in view of the aforementioned problem, and it is an object to provide a solenoid valve circuit for an automatic transmission which has a high degree of freedom in positions for mounting a solenoid valve and other valves and is capable of easily adjusting the output pressure characteristics.
According to the first aspect of the present invention, there is provided a solenoid valve circuit for an automatic transmission developing a predetermined output pressure by draining working fluid supplied from a supply pressure oil passage through an orifice, by means of a two-way solenoid valve, wherein said orifice is defined in a nozzle portion of said two-way solenoid valve.
Since the orifice is defined in the nozzle portion of the two-way solenoid valve, other additional members are particularly not needed to form the orifice and also the degree of freedom in the installation position is high. Moreover, the output pressure characteristics may be adjusted by merely replacing with a two-way solenoid valve having an orifice of a different size, as a result of which the adjustment operation is greatly simplified.
Preferably, the two-way solenoid valve has said nozzle portion and a drain port; an oil hole capable of communicating with the drain port and an orifice port being in communication with the oil hole and serving as the orifice are opened to the nozzle portion; an opening of the orifice port faces the supply pressure oil passage; and an opening of the oil hole faces an output pressure oil passage.
After the working fluid from the supply pressure oil passage has passed through the orifice port, output pressure is regulated to a predetermined pressure by properly draining the working fluid from the drain port and is provided from the oil hole to the output pressure oil passage.
Preferably, the oil hole is opened on a head of the nozzle portion; the orifice port is opened to a side of the nozzle portion; the side of the nozzle portion faces the supply pressure oil passage; and the head of the nozzle portion faces the output pressure oil passage.
Since an opening of the oil hole and an opening of the orifice port are arranged separately at the head of the nozzle portion and at the side of the nozzle portion, sealing between the supply pressure oil passage and the output pressure oil passage can be easily achieved.
The above and further objects and features of the invention will be more fully apparent from the following description when the same is considered with reference to the accompanying drawings.